Field of the Invention
The present invention relates to a liquid discharging head that discharges a liquid from plural discharge ports.
Description of the Related Art
It is advantageous to use a long liquid discharging head including an array of many discharge ports from which a liquid is discharged, in order to achieve high speed printing onto a recording medium. In particular, a full-line-type liquid discharge printing apparatus, which continuously feeds a recording medium and discharges ink for printing, uses a liquid discharging head including a long array of discharge ports having a length larger than the width of the recording medium. Such a liquid discharging head is typically configured by arranging relatively short print element substrates each including the discharge ports and heat-generating resistance elements that generate thermal energy in order to discharge the liquid from the discharge ports. This configuration enables the liquid discharging head including the long array of discharge ports to be readily provided at low cost. For the configuration of the arranged print element substrates, however, a difference in temperature that occurs in the interior of each print element substrate or among the print element substrates may cause a difference in the amount of discharged liquid. Accordingly, the difference in temperature that occurs in the interior of each print element substrate and the difference in temperature that occurs among the print element substrates need to be controlled so as to be restricted within a predetermined range.
As the liquid discharging head that performs such control, Japanese Patent Laid-Open No. 2011-240521 discloses a liquid discharging head in which each print element substrate is provided with a main channel through which a liquid is supplied and the liquid circulating through the main channel cools the print element substrates. In this liquid discharging head, heat generated by the heat-generating resistance elements when the liquid is discharged is divided into heat transferred to a support member that supports the print element substrates and heat transferred to the liquid. The heat transferred to the support member is transferred to the circulating liquid and the support member is thereby cooled. Thus, the heat generated in the print element substrates is successively transferred to the liquid via the support member, and an increase in the temperature of the print element substrates can be suppressed.
For current liquid discharge apparatuses, however, discharge frequency is further increased and the length of the liquid discharging head is further increased to achieve high speed printing and large size printing, and the number of discharges per unit time and a calorific value per unit time are likely to increase. Accordingly, the liquid discharging head disclosed in Japanese Patent Laid-Open No. 2011-240521 cannot sufficiently cool the print element substrates, and in some cases, it is difficult to restrict the difference in temperature in the interior of each print element substrate and the difference in temperature among the print element substrates to be within a predetermined range. In these cases, the amount of liquid discharged from the discharge ports in the interior of the liquid discharging head varies and this variation causes degradation in the quality of images. It is difficult to solve the problem of the variation in the amount of the discharged liquid by merely increasing the flow rate of the circulating liquid. It is known that even though the increase in the flow rate of the liquid may decrease the overall temperature of a liquid discharging head, there is almost no reduction in the difference in temperature among liquid discharging heads. Supposing a very large amount of liquid is circulated through the liquid discharging head, the difference in temperature among the liquid discharging heads can be reduced, but this needs a large pump, leading to an increase in the size of the liquid discharge apparatus and an increase in the production cost and running cost.